2 PBRs, 2 BOs 8-9 weeks old. Hens?

I am totally new to the business of chicken ownership. This spring we built a coop and picked up 4 chicks from our local feed store. 2 Plymouth Barred Rocks and 2 Buff Orphingotns. We paid extra for pre-sexed chicks, and they said there was a 90 percent chance we had hens.

Now we have 4 chickens that are almost 9 weeks old. I have the same question everyone else here has... when can I tell if one is a rooster? Would I know by now? There is a clear pecking order, but I have read that it is normal for one hen to become dominant if there is not a rooster present. The two Buffs look almost identical, and so do the 2 PBRs. I can't see any difference in comb or color, and they are similar in size. I could not find saddle feathers either. One of the PBRs is very bossy and outgoing. She is a bit bigger, and has a little bit longer tail- s/he is the one I am mostly wondering about. Is it possible that she is bigger because she is so bossy and just eats first and more? Both PBRs are much bossier, friendlier, and more outgoing the both BOs.

Here is a picture of one of the Plymouth Barred Rocks with the two Buff Orpingtons. Both PBRs are a lot bigger than the Buff Orps, even though the feed store told us that they hatched within 24 hours of one another. Is this because the Buffs are just slower at growing?

Here is a picture of the two PBRs together where you can see their faces really well:

Here is a picture of them from the side:

Thanks for your help! This is my first post... but after reading the board for a few weeks now, I am really looking forward to some input, everyone here is more experienced than me!